A multi-layer coated sodium ion battery positive electrode material, preparation method and sodium ion battery

Abstract

The present invention discloses a method for preparing a multi-layer coated sodium ion battery positive electrode material, comprising the following steps: S1. uniformly mixing transition metal oxide particles and polyanion compound particles in a first dispersion medium to obtain a first slurry; spray-drying the first slurry to obtain first particles; S2. uniformly mixing the first particles and an organic carbon source in a second dispersion medium to obtain a second slurry; spray-drying the second slurry to obtain second particles; S3. carbonizing the second particles under an inert atmosphere to obtain a multi-layer coated sodium ion battery positive electrode material. The multi-layer coated sodium ion battery positive electrode material prepared by the present invention achieves multi-dimensional improvements in material structural stability, interface stability, and rate performance. The prepared battery cell has high environmental stability and high electrochemical stability, and the preparation process is simple and the cost is controllable.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a multi-layer coated sodium ion battery positive electrode material, a preparation method thereof, and a sodium ion battery. Background Art

[0002] The research and development of lithium-ion batteries began in the 1970s. Due to their high energy density, lithium-ion batteries are widely used in transportation, power tools, 3C, and energy storage, leading to the rapid development of lithium-ion battery applications and technology. However, due to the tight supply of lithium-ion battery materials and the continuous rise in raw material prices, some researchers have turned their attention to sodium-ion batteries. Unlike lithium, sodium resources on Earth are abundant and evenly distributed globally. At the same time, because sodium-ion batteries work on similar principles to lithium-ion batteries, they can be processed and manufactured using similar processes to lithium-ion batteries, and existing lithium-ion battery production lines can be directly used. Therefore, sodium-ion batteries are considered to be a beneficial supplement to lithium-ion batteries and will gradually be used in the field of secondary batteries.

[0003] At present, the positive electrode materials of sodium ion batteries are mainly divided into transition metal oxides, polyanionic compounds and Prussian compounds, among which transition metal oxides are widely studied because of their high gram capacity; however, due to their poor reversibility during discharge, low interface stability and poor air stability, their wide application in sodium ion batteries is limited. In the prior art, coating helps to alleviate the above problems. For example, the Chinese patent with publication number CN109638273A (publication date April 16, 2019) discloses a coating method for a positive electrode material of a sodium ion battery, which uses stable metal oxides such as Al and Mg to coat transition metal oxide sodium positive electrode materials. The Chinese patent with publication number CN110277540A (publication date September 24, 2019) discloses a core-shell structure sodium ion battery positive electrode material, which is prepared by a secondary sintering method. The core-shell structure sodium ion battery positive electrode material is constructed by an O3 phase core and a P2 phase shell. However, the preparation process of these coating methods is relatively complicated and has a great impact on the intrinsic capacity of the material. At the same time, the volume expansion during the charging and discharging process cannot be alleviated. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a multi-layer coated sodium ion battery positive electrode material, which has high structural stability, high interface stability and high rate performance. The prepared battery cell has high environmental stability and high electrochemical stability, and the preparation process is simple and the cost is controllable.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a multi-layer coated positive electrode material for a sodium-ion battery, comprising the following steps:

[0007] S1. Mix transition metal oxide particles and polyanion compound particles uniformly in a first dispersion medium to obtain a first slurry; spray-dry the first slurry to obtain first particles;

[0008] S2. Mix the first particles and an organic carbon source uniformly in a second dispersion medium to obtain a second slurry; spray-dry the second slurry to obtain second particles;

[0009] S3. Carbonize the second particles under an inert atmosphere to obtain the multi-layer coated positive electrode material for the sodium-ion battery.

[0010] As a positive electrode material for a sodium-ion battery, transition metal oxides have the advantage of high specific capacity. However, their poor discharge process reversibility, low interface stability, and poor air stability limit their widespread application in sodium-ion batteries. In the present invention, transition metal oxides and polyanion particles of different particle sizes are dissolved in a solvent and rapidly dried by spray drying, so that small-sized polyanions shrink and coat on the surface of large-sized transition metal oxides, forming a primary coating; then the dried primary-coated particle powder is compounded with an organic carbon source and pyrolyzed to prepare a secondary coating material. The polyanion material coating layer formed on the surface of the transition metal oxide particles can reduce the influence of air on the transition metal oxides and improve their stability. In addition, due to the low conductivity of the polyanion material, the high conductivity of carbon compensates for the deficiency of the intrinsic conductivity of the polyanion through secondary carbon coating, ensuring the electronic conductivity of the overall particles, and at the same time further stabilizing the interface between the positive electrode material and the electrolyte, and improving the cycle performance of the battery.

[0011] Further, in step S1, the transition metal oxide is Na x M y O z , where 0.5 < x < 2, y ≥ 1, z ≥ 1, and M is one or more of Mn, Fe, Ni, Li, Mg, Cu, Ru, Co; the polyanion compound is one or more of orthophosphate, pyrophosphate, fluorophosphate, and sulfate.

[0012] The state of the coating layer significantly impacts the performance of the electrode material. Excessive coating area or excessive thickness of the coating layer can negatively impact the performance of the electrode material. Controlling the coating area and coating thickness can improve stability while ensuring the specific capacity and rate performance of the positive electrode material. In step S1 of the present invention, preferably, the D50 particle size r1 of the transition metal oxide particles is 10-15 μm, and the D50 particle size r2 of the polyanion compound particles is 0.2-7 μm, where r2 is controlled to be nr1, and n is controlled to be 2%-50%. By controlling the D50 particle sizes of the transition metal oxide particles and the polyanion compound particles, it is possible to ensure that the polyanion is coated on the surface of the transition metal oxide without causing excessive volume increase of the coated particles, excessive coating area, or excessive coating. Furthermore, layered oxides undergo volume changes during charge and discharge. A smaller polyanion coating thickness can maintain effective bulk ionic conductivity while supporting the carbon film, providing a buffer for the expansion of the layered oxide, ensuring the stability of the positive electrode material, and facilitating improved cycling performance of sodium batteries.

[0013] In addition to the D50 particle size, the number of transition metal oxide and polyanion compound ions is also related to the state of the coating layer. By controlling the number of particles, the area ratio of the coating layer can also be controlled. The number of ions can be calculated according to m = ρ * V 颗粒 *n (n is the number of ions) is estimated. In step S1 of the present invention, the ratio of the number of polyanion compound ions to the number of transition metal oxide ions is preferably 20 to 6000, for example, it can be 100, 500, 1000, 2000, 3000, 4000, 5000, etc. If the ratio of the number of polyanion compound ions to the number of transition metal oxide ions is too large, the coating layer will be too thick, the coating area will be too large, and the buffer layer will not be formed, affecting the conductivity and cycle capacity; if the ratio of the number of polyanion compound ions to the number of transition metal oxide ions is too small, the polyanion will not be able to cover the transition metal oxide core and a buffer layer will not be formed, affecting the stability of the positive electrode material.

[0014] Furthermore, in step S1, the first dispersion medium is one or more of ethanol, N-methylpyrrolidone, and acetone;

[0015] The viscosity of the first slurry is 8000-25000 mPa.s, and the proportion of the first dispersion medium is 40%-70%.

[0016] Furthermore, in step S2, the organic carbon source includes one or more of glucose and sucrose, and the second dispersion medium is water;

[0017] By controlling the mass ratio of the carbon source to the primary coating, the thickness of the surface carbon film can be effectively controlled. In the present invention, the mass ratio of the first particles to the organic carbon source is 10% to 25%. Controlling this mass ratio, combined with the subsequent spray drying process, allows the D50 of the secondary-coated positive electrode particles to be controlled within 12 to 20 μm, ensuring a sufficient carbon coating area and thus ensuring the compaction density of the positive electrode material.

[0018] Furthermore, the solid content in the second slurry is 15% to 25%.

[0019] During the spray drying process, controlling the gas-liquid ratio and drying temperature can effectively control the particle size after drying. Furthermore, in steps S1 and S2, the spray drying temperature is 100-250°C and the gas-liquid ratio is 0.2-0.5.

[0020] Furthermore, in step S3, the carbonization temperature is 200-800° C. This temperature can ensure that the carbon source precursor is fully decomposed to form a carbon film.

[0021] In a second aspect, the present invention provides a multi-layer coated sodium ion battery positive electrode material prepared by the method described.

[0022] In a third aspect, the present invention provides a sodium ion battery comprising a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the positive electrode is prepared from the multi-layer coated sodium ion battery positive electrode material.

[0023] Furthermore, the preparation method of the sodium ion battery is:

[0024] (1) The prepared multi-layer coated sodium ion battery positive electrode material, conductive agent, binder, and solvent are mixed evenly and then coated on the aluminum foil current collector and dried. Among them, the active material ratio is controlled at 90-96%, the conductive agent ratio is controlled at 2%-5%, the binder ratio is controlled at 3%-5%, the solid content is controlled at 50%-70%, the viscosity is controlled at 20000-100000 mPa.s, and the surface density is controlled at 150-250 g / m 2 .

[0025] (2) The sodium battery negative electrode, conductive agent, binder and solvent are uniformly mixed and then coated on the copper foil current collector and dried, wherein the negative electrode material can be one or more amorphous carbon materials such as soft carbon, hard carbon, composite carbon, etc.; the solid content is controlled at 45% to 60%, the viscosity is controlled at 4500 to 15000 mPa.s; the coating surface density is controlled at 100 to 150 g / m 2 , ensuring that the N / P ratio of the negative electrode / positive electrode is controlled at around 1 to 1.2.

[0026] (3) The positive and negative electrodes after coating and drying are rolled and die-cut, and then laminated with the diaphragm to form an electrode group, and then put into the shell, assembled, welded, dried, and injected with liquid. The rolling parameters are controlled at 2.6g / cm 3 -3.0g / cm 3 The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, NaCF3SO3, etc.; the solvent is one or more of EC (ethylene carbonate), DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), PC (propylene carbonate); the additive is one or more of VC (ethylene carbonate), PS, NaBOB, NaF2O2P, FEC, DTD, MMDS, etc.

[0027] (4) The battery after liquid injection is left to stand, pre-charged, exhaust gas is extracted, sealed, and capacity is divided to prepare a sodium ion battery.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. To address the shortcoming of poor interface stability of transition metal oxide materials, the present invention utilizes a composite of transition metal oxide materials and polyanion materials. The polyanion material will coat the surface of the transition metal oxide particles, reducing the impact of air on the transition metal oxide material and improving the stability of the electrode material.

[0030] 2. The present invention adopts a secondary carbon coating method based on the primary coating of the polyanion material, which can make up for the defect of low conductivity of the polyanion material and further stabilize the interface between the positive electrode material and the electrolyte.

[0031] 3. The present invention controls the D50 ratio of the coating material so that the surface of the granular material is fully coated with the polyanion material and the carbon material, while controlling the coating area and the coating layer thickness, thereby forming a volume expansion buffer layer and ensuring effective bulk ion conductivity, thereby improving the stability of the positive electrode material and the cycle performance of the sodium battery.

[0032] 4. The multi-layer coated sodium ion battery positive electrode material prepared by the present invention realizes controllable coating area and coating thickness by controlling the coating particle size ratio, the coating particle number ratio and the carbon film ratio. At the same time, the multi-layer coating space formed by the coated polyanion particles as a support provides space for the volume expansion of the layered oxide during the discharge process, thereby achieving multiple improvements in material structure stability, interface stability and rate performance. The prepared battery has high environmental stability, high electrochemical stability, and the preparation process is simple and the cost is controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the preparation process of multilayer composite sodium ion battery positive electrode materials;

[0034] Figure 2 This is a normal temperature rate performance diagram of Example 1;

[0035] Figure 3 This is the normal temperature rate performance diagram of Comparative Example 1;

[0036] Figure 4 This is the normal temperature rate performance diagram of Comparative Example 2;

[0037] Figure 5 It is a normal temperature cycle performance diagram of Example 1-3 and Comparative Example 1-2. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0041] Example 1

[0042] This embodiment provides a method for preparing a sodium ion battery, comprising the following steps:

[0043] 1. Select the transition metal oxide positive electrode material Na with D50 of 10μm 0.67 MnO2, orthophosphate polyanion cathode material NaFePO4 with D50 of 0.5 μm and ethanol solvent are uniformly mixed to form a slurry, and the solid content of the slurry is controlled to be 60%; wherein the number of NaFePO4 particles is Na 0.67 1350 times that of MnO2;

[0044] 2. Prepare the mixed solution into a primary coating precursor by spray drying, wherein the drying temperature of the spray drying is 100°C and the gas-liquid ratio is controlled at 0.3;

[0045] 3. The dried powder and glucose carbon source were evenly dissolved in water and mixed, wherein the glucose accounted for 10% and the solid content was 15%. The secondary coated positive electrode particles with a D50 of 18 μm were prepared by spray drying, wherein the drying temperature of the spray drying was 150 ° C;

[0046] 4. Carbonizing the secondary coated particles in an inert gas atmosphere at a carbonization temperature of 700°C;

[0047] 5. The carbonized secondary coating active material, conductive agent and binder are mixed in a ratio of 92:4:4 to prepare a slurry, which is then coated on the aluminum foil current collector. The solid content is controlled at 60%, the viscosity is controlled at 25000mPa.s, and the coating surface density is controlled at 180g / m 2 ;

[0048] 6. Mix the hard carbon, conductive agent, binder and solvent evenly and apply them on the copper foil current collector. Dry them to prepare the negative electrode sheet. The coating surface density is 100g / m 2 , control the positive and negative electrode N / P to 1.08;

[0049] 7. Roll and die-cut the positive and negative electrodes after coating and drying (the compaction density is controlled at 2.8g / cm 3 ), after laminating with the diaphragm to form an electrode group, it is then placed in the shell, assembled, welded, dried, and injected with liquid;

[0050] 8. The battery after liquid injection is placed in a static state, pre-charged, exhaust gas is extracted, sealed, and capacity is divided to prepare a sodium ion battery.

[0051] Example 2

[0052] This embodiment provides a method for preparing a sodium ion battery, comprising the following steps:

[0053] 1. Select the transition metal oxide positive electrode material Na with D50 of 13μm 2 / 3 Mn 0.5 Fe 0.5 O2, D50 of 0.5μm orthophosphate polyanion cathode material Na3V2(PO4)3 and ethanol solvent are uniformly mixed to form a slurry, and the solid content of the slurry is controlled to be 50%; wherein the number of Na3V2(PO4)3 particles is Na 2 / 3 Mn 0.5 Fe 0.5 2000 times that of O2;

[0054] 2. Prepare the mixed solution into a primary coating precursor by spray drying, wherein the drying temperature of the spray drying is 150°C and the gas-liquid ratio is controlled at 0.5;

[0055] 3. The dried powder and sucrose carbon source were evenly dissolved in water and mixed, wherein the sucrose content was 12% and the solid content was 20%. The secondary coated positive electrode particles with a D50 of 14 μm were prepared by spray drying, wherein the drying temperature of the spray drying was 150 ° C;

[0056] 4. Carbonize the secondary coated particles in an inert gas atmosphere at a carbonization temperature of 500°C;

[0057] 5. The carbonized secondary coating active material, conductive agent and binder are mixed in a ratio of 92:4:4 to prepare a slurry, which is then coated on the aluminum foil current collector. The solid content is controlled at 55%, the viscosity is controlled at 30000mPa.s, and the coating surface density is controlled at 180g / m 2 ;

[0058] 6. Mix the hard carbon, conductive agent, binder and solvent evenly and apply them on the copper foil current collector. Dry them to prepare the negative electrode sheet. The coating surface density is 98g / m 2 , control the positive and negative electrode N / P to 1.08;

[0059] 7. Roll and die-cut the positive and negative electrodes after coating and drying (the compaction density is controlled at 2.8g / cm 3 ), after laminating with the diaphragm to form an electrode group, it is then placed in the shell, assembled, welded, dried, and injected with liquid;

[0060] 8. The battery after liquid injection is placed in a static state, pre-charged, exhaust gas is extracted, sealed, and capacity is divided to prepare a sodium ion battery.

[0061] Example 3

[0062] This embodiment provides a method for preparing a sodium ion battery, comprising the following steps:

[0063] 1. Select NaNi, a transition metal oxide cathode material with a D50 of 15 μm 0.5 Mn 0.5 O2, pyrophosphate polyanion cathode material Na2FeP2O7 with D50 of 1 μm and ethanol solvent are uniformly mixed to form a slurry, and the solid content of the slurry is controlled to be 50%; wherein, the number of Na2FeP2O7 particles is NaNi 0.5 Mn 0.5 500 times that of O2;

[0064] 2. Prepare the mixed solution into a primary coating precursor by spray drying, wherein the drying temperature of the spray drying is 125°C and the gas-liquid ratio is controlled at 0.5;

[0065] 3. The dried powder and sucrose carbon source were evenly dissolved in water and mixed, wherein the sucrose content was 20% and the solid content was 25%. The secondary coated positive electrode particles with a D50 of 20 μm were prepared by spray drying, wherein the drying temperature of the spray drying was 150 ° C.

[0066] 4. Carbonizing the secondary coated particles in an inert gas atmosphere at a carbonization temperature of 800°C;

[0067] 5. The carbonized secondary coating active material, conductive agent and binder are mixed in a ratio of 92:4:4 to prepare a slurry, which is then coated on the aluminum foil current collector. The solid content is controlled at 65%, the viscosity is controlled at 28000 mPa.s, and the coating surface density is controlled at 180 g / m 2 ;

[0068] 6. The hard carbon, conductive agent, binder and solvent are evenly mixed and coated on the copper foil current collector, and dried to prepare the negative electrode sheet. The coating surface density is 96g / m 2 , control the positive and negative electrode N / P to 1.08;

[0069] 7. Roll and die-cut the positive and negative electrodes after coating and drying (the compaction density is controlled at 2.8g / cm 3 ), after laminating with the diaphragm to form an electrode group, it is then placed in the shell, assembled, welded, dried, and injected with liquid;

[0070] 8. The battery after liquid injection is placed in a static state, pre-charged, exhaust gas is extracted, sealed, and capacity is divided to prepare a sodium ion battery.

[0071] Comparative Example 1

[0072] 1. Select the transition metal oxide positive electrode material Na with D50 of 10μm 0.67 MnO2, conductive agent and binder were mixed in a ratio of 92:4:4 to prepare a slurry, which was then coated on an aluminum foil current collector. The solid content was controlled at 62%, the viscosity was controlled at 22000 mPa.s, and the coating surface density was controlled at 180 g / m 2 ;

[0073] 2. Mix the hard carbon, conductive agent, binder and solvent evenly and apply them on the copper foil current collector. Dry them to prepare the negative electrode sheet. The coating surface density is 100g / m 2 , control the positive and negative electrode N / P to 1.08;

[0074] 3. Roll and die-cut the positive and negative electrodes after coating and drying (the compaction density is controlled at 2.8g / cm 3 ), after laminating with the diaphragm to form an electrode group, it is then placed in the shell, assembled, welded, dried, and injected with liquid;

[0075] 4. The battery after liquid injection is placed in a static state, pre-charged, exhaust gas is extracted, sealed, and capacity is divided to prepare a sodium ion battery.

[0076] Comparative Example 2

[0077] 1. Select the transition metal oxide positive electrode material Na with D50 of 10μm 0.67 MnO2, orthophosphate polyanion positive electrode material NaFePO4 with D50 of 2μm, conductive agent and binder are mixed in a ratio of 92:5:4 to prepare a slurry, which is coated on the aluminum foil current collector. The solid content is controlled at 59%, the viscosity is controlled at 22000mPa.s, and the coating surface density is controlled at 180g / m 2 ;

[0078] 2. Mix the hard carbon, conductive agent, binder and solvent evenly and apply them on the copper foil current collector. Dry them to prepare the negative electrode sheet. The coating surface density is 100g / m 2 , control the positive and negative electrode N / P to 1.08;

[0079] 3. Roll and die-cut the positive and negative electrodes after coating and drying (the compaction density is controlled at 2.8g / cm 3 ), after laminating with the diaphragm to form an electrode group, it is then placed in the shell, assembled, welded, dried, and injected with liquid;

[0080] 4. The battery after liquid injection is placed in a static state, pre-charged, exhaust gas is extracted, sealed, and capacity is divided to prepare a sodium ion battery.

[0081] Performance Testing

[0082] The sodium ion batteries prepared in Example 1 and Comparative Examples 1-2 were tested for room temperature rate performance. The results are as follows: Figure 2-4 As shown in the figure, it can be seen that the multi-layer coated sodium cathode material has better rate performance, and the capacity retention rate of 1C is increased from 73.93% to 89.96%.

[0083] The sodium ion batteries prepared in Examples 1-3 and Comparative Examples 1-2 were tested for room temperature cycling performance. Figure 5 As shown in the figure, the sodium ion battery prepared by the method of the present invention has good cycle stability, and the capacity retention after 200 cycles is increased from 83% to 96%, which is significantly better than that of comparative examples 1-2.

[0084] The sodium ion battery electrodes prepared in Examples 1-3 and Comparative Examples 1-2 were placed in a room temperature -20°C dew point environment for different periods of time to test the capacity of the electrodes and verify the stability of the materials. The results are shown in Table 1.

[0085] Table 1 Gram capacity of sodium ion battery electrodes prepared in Examples 1-3 and Comparative Examples 1-2 after being left aside

[0086]

[0087]

[0088] From the results in Table 1, it can be seen that the electrode prepared by the method of the present invention has good environmental stability.

[0089] In summary, the multi-layer coated sodium ion battery positive electrode material obtained by the secondary coating method of the present invention has high environmental stability, high electrochemical stability and moderate ionic conductivity, which helps to improve the rate performance and room temperature cycle performance of the sodium ion battery.

[0090] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for preparing a multi-layer coated sodium ion battery positive electrode material, characterized in that: The following steps are involved: S1. Transition metal oxide particles Na with a D50 of 13 μm 2 / 3 Mn 0.5 Fe 0.5 O2, D50 of 0.5 μm polyanion compound particles Na3V2(PO4)3 are mixed evenly in ethanol to obtain a first slurry, wherein the number of Na3V2(PO4)3 particles is Na 2 / 3Mn 0.5 Fe 0.5 O2 2000 times; spray drying the first slurry at 150 ° C. and a gas-liquid ratio of 0.5 to obtain first particles; S2. The first particles and the sucrose carbon source are mixed uniformly in water to obtain a second slurry; the second slurry is spray-dried at 150° C. to obtain second particles; S3. Carbonizing the second particles at 500° C. under inert atmosphere to obtain the multi-layer coated sodium ion battery positive electrode material.

2. The multi-layer coated sodium ion battery positive electrode material prepared according to the method of claim 1.

3. A sodium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode, characterized in that: The positive electrode is prepared from the multi-layer coated sodium ion battery positive electrode material according to claim 2.

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